https://twitter.com/modernserf/status/1079566530202030080

1.js

const isolate = (scope) =>
  new Proxy(scope, { 
    has: () => true, 
    get: (target, key) => {
      if (key === Symbol.unscopables) { 
        return undefined 
      }
      if (key in target) { 
        return  target[key] 
      } 
      throw new ReferenceError(`${key} is not defined`) 
    } 
  })

with (isolate({ console, foo: "foo" })) {
  console.log(foo) // "foo"
  console.log("bar") // "bar"
  console.log(window) // ReferenceError "window is not defined"
}
      

2.js

const isolate = (source, ...exposedVariables) =>
  new Proxy(source, { 
    has: (_, key) => !exposedVariables.includes(key), 
    get: (target, key) => {
      if (key === Symbol.unscopables) { 
        return undefined 
      }
      if (key in target) { 
        return target[key] 
      }
      throw new ReferenceError(`${key} is not defined`) 
    } 
  })


let foo = 1
let bar = 2
let baz = 3
with (isolate(Math, "console", "foo", "bar")) { 
  console.log(min(foo, bar)) // 1
  console.log(min(bar, baz)) // ReferenceError: baz is not defined
}